In wide area trunked radio systems that utilize a feature such as Automatic Multiple Site Switching (hereinafter referred to as "AMSS") an entire area such as an entire state can belong to one system comprised of multiple sites. AMSS allows communications to be extended beyond the reach of a single trunked site (repeater antenna facility). AMSS automatically switches a radio to a different site when the current site signal becomes to weak, which is usually determined by measuring the received signal strength (RSS) level at the radio. Typically, this happens when the vehicle the radio is in is driven out of range of one site and into the range of another site.
Any subscriber radio sending in a channel request would be granted a channel on all sites simultaneously when any channel becomes available in the system, thus enabling the radio operator to maintain communication with his radio talkgroup throughout the wide area system. Though such systems provide communication throughout the entire wide area covered by the system, it also results in waisted channel allocation (lowers spectrum efficiency of the system) since all members of a particular talkgroup are generally confined to a relatively small number of sites within the overall system.
In communication systems such as cellular systems and more sophisticated trunking systems, all subscriber radios must "register" within the site that they are currently located in. This registration process informs the system controller of where each radio in a system is located (which specific site). Thus, when a channel request is received at the system controller, it can then identify which sites have to have a channel allocated for the transmission to occur. In a typical cellular system, only the site where the requesting unit is located and the site of the receiving unit have to have a channel allocated (in the case of a cellular to cellular call). In the case of a trunked system, only the sites where radios that belong to the same talkgroup have to be allocated a channel for communication to occur, thereby increasing the overall spectrum efficiency of the system(no need to allocate a channel at each site).
If a subscriber radio changes sites during a conversation, it is imperative that it register as quickly as possible on the new site, because if it is the only member of the active call's talkgroup (in the case of a trunked system) on that site, a channel will not be assigned for the call until the system is informed that a member of the talkgroup is now present on the site. Whenever a subscriber radio changes sites, it's registration on the new site automatically deregisters it on the old site.
However, if a radio is turned off, or is changed to a different system by the operator, the radio will deregister on the system, informing the system that this particular ID is no longer active on the system. If a deregistering radio is the only member of the talkgroup within the site it deregisters on, the system will drop any active call to that talkgroup on that site and will not assign a channel on that site for the active talkgroup until a member of the talkgroup again registers on that site. If somehow, a subscriber radio becomes active on a site as the only member of his talkgroup on that site and the system was for some reason not aware of this unit, or considered this unit to be registered to a different talkgroup, channels would not be assigned on that site for the radio's talkgroup and the radio would miss all talkgroup traffic until the situation was remedied.
In radio communication systems such as trunked radio communication systems that require rapid site registration, it is possible for a radio to register in a wrong system. This improper registration cannot be corrected with a normal "deregistration" sequence as used in the prior art, as this might deregister a valid radio presently on that system. This can occur if a radio on an adjoining system has the same unit ID information as the radio that registered incorrectly. Since radio communications systems are the backbone of communications for such groups of users as police officers, fireman and the like, it becomes very important, if not critical, that the above mentioned registration problems do not occur. A need exists in the art for a method and system for properly deregistering an incorrectly registered radio and at the same time re-registering any radios having the same "valid" radio ID back into the system.